In 1940 the US government commissioned the Columbia Resin Project to create glass-reinforced plastic fuel tanks instead of steel for the B-17 bomber. The goal of course was to reduce weight and ultimately increase the range the plane could fly during bombing missions. The result was CR39 Resin and interesting enough the name simply refers to the 39th formula developed as part of the Columbia Resin Project.
So how did Cokin end up using it for its filters?
Well, shortly after the end of WWII they began to look for other uses for CR39 and soon discovered that it tested very well as an optical substitute for glass. After years of rigorous testing conducted at different independent labs CR39 was determined to be an optical grade material and only second to glass at the time. Making it perfect for lightweight eyeglasses and of course Cokin photographic filters.
Here is what the testing of CR39 determined:
- It is Colorless
- Is Half the weight of glass
- 0% light transmittance below 380nm making it fully UV-B absorbent
- Highest abrasion/scratch resistance of any uncoated optical polymer
- High Refraction index of 1.49 and only marginally lower than glass
- Very low chromatic aberration and distortion
- Accept dyes extremely well
- It is resistant to most solvents and chemicals
- It can be used continuously in temperatures up to 212F (100C) and for up to one hour at 266F (130C).
In 1978 Cokin founder Jean Cokin was looking for the best material to use for his new filter company. He tested many different resins before selecting CR39 for its optical clarity, stability and durability. But it was the resin’s ability to accept Cokin’s color tinting process that sealed the deal and the first modern drop-in filter company was born.
CR39 Resin is still used today by Cokin because it is the best low-cost alternative to using glass and we can do some really cool colored effects that cannot be done with glass without breaking a lot of important environmental safety laws.
So next time you reach for your Cokin filters know that we are using the best resin material available to help you create the most unique "in-camera" effects without compromise.